Ah yep sorry got it half asleep ... still that's a lot harder than chain fishing or dexnav ... as soon as you encounter a pokemon that doesn't call for help or the call fails your chain breaks? :\

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it does not brake. You could use an antidote on one of your mons which is not poisoned. It wastes one turn but the antidote will still be in your backpack.
There also is this orbthing,forgot the name, which makes the wild Pokémon nervous and more likely to call for help.